Nadya McCann and son Miles McCann Robinson used the Nextdoor site to alert neighbors when he contracted meningitis last year.

Photo: Lance Iversen, The Chronicle

Nadya McCann and son Miles McCann Robinson used the Nextdoor site...

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Nadya McCann and her son Miles, who contracted meningitis last year, used the social media site Nextdoor.com to alert neighbors and several of Miles' friends into preventive treatment so they wouldn't get sick, too.

The Bay Area is still six or eight weeks from the start of the flu season, but when it finally strikes, the Internet will probably be the first to know.

Before state and local public health departments detect an outbreak - often days or weeks before the U.S. Centers for Disease Control and Prevention is made aware - many people who feel themselves coming down with the flu will post something about it to Twitter or Facebook.

Or they'll search Google for advice on lowering a fever or to find out the hours of their neighborhood pharmacy.

Public health experts know the secret to effective, proactive disease surveillance is getting clues of an impending outbreak before it can spread far and wide. To that end, their official surveillance tools have improved dramatically in recent years, but to gain an additional edge, they also are looking to the Internet, and social media in particular, as a possible warning system from the front lines.

"Public health agencies are limited by resources and funding. We can't be everywhere, every time," said Dr. Charles Chiu, an infectious disease expert at UCSF. "Social media provides an excellent means of monitoring outbreaks before they spread. You could track the emergence of an epidemic before you even know the cause of it."

Already, studies have shown that Google Flu Trends - a project developed to monitor disease activity based on queries for things like "muscle aches" and "thermometer" - is able to produce results similar to the CDC, but a week or more earlier. The CDC surveys national flu activity based on reports from doctors, hospitals and laboratory results.

This month, a Bay Area company began promoting in San Francisco a new website - FluNearYou.org - that encourages users to check in every week and report whether they're sick with flu-like symptoms.

Meanwhile, infectious disease experts increasingly are looking at Twitter to identify the earliest stages of cholera and dengue fever outbreaks in developing countries where public health resources for surveillance are extremely limited, but almost everyone has a cell phone and Internet access.

"I look at Google Flu Trends and see a blip and say, 'Hmm, I wonder what's happening there?' " said Lynnette Brammer, an epidemiologist in the influenza division at the CDC.

"The hope is that these systems might give us a little bit of an edge, time-wise, over virologic surveillance," Brammer said. "You're constantly taking clues from different pieces and trying to put them together. The more pieces you have, the more you can come up with a right answer."

Disease surveillance has always been a critical tool in protecting public health. Health experts can identify outbreaks of contagious illnesses and, in turn, take measures to prevent illness in those who aren't sick and gather resources to treat those who are.

For something widespread and highly infectious like influenza, it's impossible to report and collect every case, as public health departments do for whooping cough, measles, meningitis and many of the most serious diseases. So public health officials rely on complex surveillance mechanisms to estimate the spread and severity of disease.

Electronic reporting

Surveillance tools have improved in recent years - mostly because of electronic reporting, faster, more accurate lab tests and a better understanding of infectious disease patterns - but they still often lag just behind an outbreak.

When the swine flu hit in 2009, for example, speedy surveillance systems allowed federal and state public health officials to identify the first case in the country and spread word to the public within a few weeks to take precautionary measures. Still, by the time that first case was found, the new flu virus already had spread throughout the state.

Tracking social media or other online sources before the swine flu outbreak might have alerted public health officials to an unusual spike in cases weeks before it reached epidemic levels, according to a 2011 study. There's no way of knowing whether that knowledge could have prevented the epidemic or saved lives, but earlier awareness is always the goal of disease surveillance, public health officials say.

"The closer you can get to the person who's actually experiencing an illness, the sooner you're going to find out that something is going on," said Dr. James Watt, chief of the division of communicable disease control in the California Public Health Department's center for infectious diseases. "There's a lot of potential in social media. I'm sure we'll find new methods we can use to track flu."

Several studies looking back at recent disease outbreaks have shown that social media and other Internet platforms were able to accurately track activity faster than traditional surveillance tools.

During a cholera outbreak in Haiti in 2010, references to "cholera" on Twitter reflected the actual number of cases in the community, and had public officials detected it, they could have tracked the disease activity, according to one study. Another study found that a search of media reports on "listeriosis" in 2008 detected early signs of a listeria outbreak that year in Canada two months before an official public report was made.

That kind of early detection could be especially beneficial in developing countries, Chiu said.

"They may not have infrastructure for quickly diagnosing diseases, but they at least have access to social media," he said. "A large percentage of the population has a mobile phone and Twitter."

Vulnerable to error

Google Flu Trends, for example, has proven to be a good tracker of influenza activity overall, but can show false positives. Not everyone who searches for flu symptoms is actually sick with the flu - they could have a cold or any number of flu-like viruses. They may not be sick at all.

Websites that require self-reporting, such as the new FluNearYou site, may never provide an accurate sense of disease activity if users aren't representative of the community as a whole.

For the moment, public health officials who use social media and other online surveillance are usually treating it more as a curiosity than anything else, they say. Or it's serving perhaps as a reminder to them to look at their own data more closely if they notice an unusual trend.

Truth in lab reports

"Google might get an earlier signal about influenza than us. The problem is so many of their early signals will be false signals," Baxter said. "At Kaiser, we follow a thing called 'percent positive' - if 100 tests come in but only two are positive for influenza, we know there are respiratory viruses out there but it's not flu. I would know before Google if there was a true outbreak."

But in the not-too-distant future, many infectious disease experts say, social media could be integrated with traditional surveillance tools to develop a faster, more detailed method of predicting and identifying outbreaks.

"The ultimate goal would be to look for trends with social media and then get hard data to validate those trends," Chiu said. "It's very similar to monitoring for terrorist activity. What you're looking for are spikes of data that will tell you where to pay attention."

Another advantage of online surveillance sites is that they tend to be more easily accessible to the public. FluNearYou, its creators say, allows people to see what's happening in their immediate community.

Even websites that weren't necessarily designed with public health in mind are proving to be valuable tools in unexpected ways.

Last summer, a Woodside mom used the social-media site Nextdoor.com to alert her neighbors that her teenage son had contracted a highly contagious form of meningitis, and that anyone who had been in contact with him recently may need preventive care.

"I had no idea how to reach everyone he'd been around. So I just posted something on Nextdoor," said Nadya McCann, whose son, Miles McCann Robinson, is healthy now. "And thank God I did, because many of these kids ended up taking prophylactic antibiotics.

"I don't know if we prevented an outbreak," McCann said. "But without social media, those kids would not have gotten antibiotics. We don't know what would have happened."